Oregon's longest-tenured congressman faces a second consecutive challenge from a Republican chemist with tea party support in what is expected to be the closest of the state's five U.S. House races.

Tuesday's vote will be Republican Art Robinson's second attempt to unseat Democrat Peter DeFazio. DeFazio represents the timber-dependent 4th Congressional District, often finding himself fending off both environmental advocates and the timber industry. DeFazio was first elected to the U.S. House in 1986.

Robinson pledges to cut taxes, increase border security and build new power plants. He lost to DeFazio in 2010 by a wide margin but enjoys financial support from tea party advocates, people who deny human involvement in climate change and home-schooling advocates.

In the swing 5th District, Democrat Kurt Schrader is running for a third term, against Republican Fred Thompson.

The Oregon GOP has long targeted the 5th Congressional District because of its near-split between Democrats and Republicans. The GOP's candidate in 2010 was a legislator, Scott Bruun, who came within a few percentage points.

Their candidate this year, Fred Thompson, a retired Army sergeant, was president and chief executive of a company that converted agricultural waste into building materials.

Schrader, a veterinarian, has joined with the Blue Dog Coalition of fiscally-conservative Democrats.

Suzanne Bonamici, a Democrat, won a special election in January to replace former Rep. David Wu in the 1st Congressional District. She faces Delinda Morgan for her chance at a full term.

In her brief time in office, Bonamici has focused on supporting education and issues that affect high-tech companies. She also introduced legislation to help deal with wreckage from the Japanese earthquake that's washing up along the coast.

Morgan is a former heavy equipment operator who owns a vineyard with her husband. Morgan said she would be an advocate for small business owners by cutting regulations and getting rid of President Barack Obama's health care law.